1. Field of the Invention
The present invention relates generally to a linear motion guide unit adapted for use in various types of machinery such as semiconductor manufacturing machines, precision measuring instruments, precision inspection equipment, precision assembly machines, machine tools, industrial robots or the like and, more particularly, to a linear motion guide unit that is provided therein with means for keeping a cage against wandering.
2. Description of the Prior Art
Current linear motion guide units of the type where rolling elements are allowed to roll over only a definite travel instead of rolling through a recirculating circuit have been used extensively in diverse fields of machinery such as semiconductor manufacturing machines to guide a part in a linear way relatively to any counterpart. To this end, the linear motion guide units of the sort recited just above are seeing growing demands for high speed operation and high acceleration/deceleration, with even made slim or compact in construction. At the same time the advanced machinery expects the linear motion guide units to be operated with high precision and low-frictional resistance. Solving the issues stated earlier is needed for further development of the linear motion guide units.
Disclosed in Japanese Patent Laid-Open No. 108056/1999 is a linear motion guide unit of the type recited earlier, which has a means for keeping a cage or retainer against wandering to help control certainly the travel of guide rail members. The cylindrical rollers held in the cage are placed for rolling between confronting raceway grooves formed on the guide rail members. The cage has supported a pinion for rotation, which comes in mesh with a rack of gear teeth held in a gutter for relief. With the linear motion guide unit recited earlier, the teeth on the rack are made recessed to avoid any interference with the cylindrical rollers. This construction allows the rack of gear teeth to be made in a module large in size, thus increasing the strength in mesh with the pinion thereby to keep the cage against wandering with respect to the associated guide rail members. The prior construction, as having no need of making the gutter for relief large, also can ensure the wider guide surface.
In Japanese Patent Laid-Open No. 315831/1999 there is disclosed a linear motion guide system with a cage that can be positively guided so as to move with no wander. The prior linear motion guide unit has two guide rails arranged in opposition for lengthwise movement relatively to one another, and rolling elements held in a cage with being interposed between the confronting guide raceways on the guide rails. The cage is provided with at least one pinion to lead positively the cage. The gear wheel comes in mesh with racks of teeth gear, which are arranged to the guide rails, one to each rail.
The same sort of linear motion guide system is also disclosed in Japanese Patent Laid-Open No. 315832/1999.
In every prior linear motion guide systems recited earlier, nevertheless, the pinion or gear wheel is supported for rotation by a pair of gear holders that are in turn made into engagement with latch pawls of the cage. The construction, despite involving more sophisticated chores for assembly of the gear holder, couldn't make regularly certain of secure engagement of the gear holder. Moreover, the prior linear motion guide units of the sorts stated earlier, as the rack and the pinion are made relatively complicated in their tooth profile, are apt to encounter large sliding resistance and also very tough to shrink the guide unit itself in construction.
With the rack-and-pinion arrangement used in the conventional linear motion guide units, the pinion has a circular plate around which rolling elements are positioned at regular intervals, with extending somewhat radially outwardly beyond the outermost periphery of the circular plate. The rack is made with recesses that are arranged at regular intervals parallel with the radially extending rolling elements. This rack-and pinion arrangement stated just earlier involves a chore to make a series of recesses on the rack in line with the teeth of the pinion and also needs sophisticated machining and forming operations to make sure of accurate mating between the associated teeth of the rack and the pinion.